1. Field of the Invention
The invention relates generally to pipe couplings and more specifically to an improved coupling which is used to connect pipe sections, wherein each of the pipe sections has a integral buoyancy can surrounding the pipe.
2. Related Art
Pipelines are commonly used to transport oil and other is hydrocarbons. Because of the enormous quantities of oil and/or hydrocarbons which need to be transported in this manner, the pipelines are typically constructed on a correspondingly large scale.
Pipelines of this type normally formed by a series of pipe segments, or sections. The pipe sections are individually manufactured, then transported to the site where the pipeline will be installed. At the installation site, the pipe sections are aligned and joined together to form the single conduit of the pipeline. The pipe sections normally include a flange at each end which can be coupled (e.g., bolted) to a corresponding flange of an adjacent pipe section. The pipe sections may, for example, utilize standard ANSI flanges.
Because of the scale of these pipelines, it may be very difficult to work with the pipe sections. The immense weight of individual pipe sections, for example, may make it difficult to suspend them so that they can be properly oriented before bolting them together. One way to make it easier to manipulate the pipe sections in a marine environment is to construct the pipe sections with integral buoyancy cans. The buoyancy cans increase the volume of the pipe sections so that they displace more water and, as a result, become more buoyant.
Referring to FIG. 1, a cross-sectional diagram illustrating a prior art structure of a pipe section having a buoyancy can is shown. Only one end of pipe section 10 is shown in the figure. The opposite end of the pipe section would normally be a mirror image of the illustrated end. Pipe stem 12 forms the conduit 13 through which fluid will be transported in the assembled pipeline. At each end of pipe stem 12 is a flange 14. As noted above, flange 14 may be an ANSI flange or any other flange which is used in the industry.
The buoyancy can comprises an outer, cylindrical wall 16 to which a plate 18 is connected at each end. Cylindrical wall 16 and end plate 18 are typically welded together. End plate 18 is also welded to pipe stem 12, which extends through the aperture in the center of the annular plate. Together, pipe stem 12, cylindrical wall 16 and end plates 18 form a cavity 19. When pipe section 10 is submerged, the buoyancy displaces a volume of water approximately equal to the volume of cavity 19, making the pipe section more buoyant and more easy to manipulate.
Although these pipe sections are manufactured with buoyancy cans, they are typically still coupled to each other in the same manner as pipe sections which do not have buoyancy cansxe2x80x94using standard bolted flanges. Referring to FIG. 2, a diagram illustrating a pair of coupled pipe sections is shown. One of the problems with coupling pipe sections 10 and 20 together in this manner is that, while the pipe sections are more buoyant than pipe sections that do not incorporate buoyancy cans, they are nevertheless heavier and subject to greater inertia. Further, because of their larger size, the pipe sections having buoyancy cans are subject to greater environmental forces, such as ocean currents. Consequently, the couplings of these pipe sections may be subject to greater stresses which may result in a higher rate of failure of the couplings.
It would therefore be desirable to provide a coupling for pipe sections having integral buoyancy cans, wherein the coupling is configured to handle the higher stresses associated with this type of pipe section.
One or more of the problems outlined above may be solved by the various embodiments of the invention. Broadly speaking, the invention comprises a coupling for two pipe sections having integral buoyancy cans, wherein the coupling includes an inner flange configured to couple the pipe stems of the pipe sections and an outer flange configured to brace or secure the buoyancy cans of the pipe sections against each other and thereby stabilize the pipe sections.
In one embodiment, the coupling comprises a pair of flanges, each of which is attached to one of a pair of pipe sections. Each of the pipe sections has a pipe stem and a cylindrical buoyancy can which is positioned coaxially with the pipe stem. Each of the flanges has an inner flange portion and an outer flange portion. The inner flange portions are connected to the pipe stems of the respective pipe sections. Each of the inner flange portions is configured as a female box flange. When the coupling is assembled, a pin flange is positioned between the inner flange portions to form what is essentially a pin-and-box connection. The outer flange portions are positioned near the outer edges of the respective buoyancy cans. When the coupling is assembled, the outer flange portions are secured together, thereby securing the buoyancy cans of the pipe sections together and stabilizing the coupling, including the connection between the inner flange portions.
In one embodiment, the inner and outer flange portions of each pipe section are connected by a first annular plate that forms the end of the buoyancy can. The inner and outer flange portions extend forward from the first annular plate (away from the buoyancy can) and are also connected by a second annular plate which is positioned near the forward end of the flange portions. A cavity is thereby formed between the inner and outer flange portions and between the first and second annular plates. A plurality of reinforcing plates are positioned in the cavity and attached to the flange portions and the annular plates. These reinforcing plates are oriented so that they are co-planar with the axis of the pipe section to provide additional strength in the flange assembly.
The present coupling may provide a number of advantages over the prior art. For example, the present coupling may be better able to withstand bending stresses between the pipe sections because of the larger overall diameter of the coupling. Further, because each of the flange assemblies forms a box flange for a pin-and-box coupling, the flange assemblies have no protruding surfaces which might be easily damaged during manufacture or shipping. Further, the present coupling may eliminate the need for a separate end plate to be welded to the buoyancy can to hold it in position around the pipe stem (since the coupling itself serves this function.) Still further, the present coupling may make it easier to position the pipe sections for assembly because the flanges are bolted together near the outer diameter of the buoyancy can, rather than near the pipe stem (thereby eliminating the need for a worker to position himself between the buoyancy cans while bolting the flanges together.